#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int main()
{
	int j = 0;
	int k = 0;

	for (int i = 20; i > 0; i--)
	{
		j++;
		k++;
		if (k % 2 == 0)
		{
			i++;

		}
		
	}
	printf("%d", j);
	return 0;
}